Measures assessing the quality of children's environments and interactions in nonparental care settings were developed originally for use in child care research and as self-assessment tools for practitioners. Within the last decade, these measurement tools have moved into the public policy arena, where they are now used to make programmatic decisions and inform consumers about the quality of settings. As new demands are placed on quality measures to be used in accountability systems, questions emerge about how measures function in these new contexts and in what ways measurement strategies could be strengthened. This brief provides an overview of what we know and what we don't know, given the current status of the research, about three key questions concerning the measurement of quality: (1) What aspects of quality are important to measure? (2) What aspects of quality are well-covered by exiting measures and (3) What measurement strategies are most effective in state quality improvement initiatives and rating systems? It also provides suggestions for ongoing research and dialogue related to each question. (Contains 11 endnotes.)